The subject matter disclosed herein relates to a method of operating a combustor for a gas turbine from a liquid fuel operation to a gas fuel operation.
Gas turbines include one or more combustors, which receive and combust air and fuel to produce hot combustion gases. For example, the gas turbine may include multiple combustion chambers positioned circumferentially around a rotational axis. Either a liquid fuel or a gas fuel may be injected into the combustor. In the event that the gas turbine is operating on liquid fuel and a transfer to gas fuel is required, the liquid fuel flow is first shut off or stopped, and then a purge fluid is sent through liquid fuel nozzles. The purging fluid removes any residual liquid fuel from the liquid fuel nozzles. There can be a delay between shutting of the liquid fuel flow and sending the purging air through the liquid fuel nozzles at a high enough flow rate or pressure. In the event a flame is anchored on the liquid fuel nozzles during the delay, a resulting pressure gradient may send hot combustion products into the liquid fuel nozzle, which in turn may cause damage.
In some types of combustion systems such as, for example, dry low NOx combustion systems, the combustor may only transfer from liquid fuel operation to gas fuel operation at a relatively low load. The transfer between the liquid fuel and the gas fuel may be performed, but requires unloading the gas turbine to the reduced load first. In a combined cycle power plant, unloading the gas turbine to a low load may also require for a steam turbine to taken off-line as well.